This invention relates to an improved lubricating grease composition and more particularly to a grease composition having improved extreme pressure properties and comprising an additive package which contains a selected oil insoluble phosphorus compound and an oil soluble sulfur compound.
It is, of course, well known in the prior art that various metal soaps can be advantageously used in the preparation of lubricating greases from essentially any lubricating base oil stock and that the greases thus prepared will, generally, exhibit good grease properties and/or characteristics. While a number of grease compositions have been prepared with different combinations of metal soap thickening agents and base oils, there has been particular difficulty in obtaining a grease composition suitable for use in severe applications where extreme pressure properties are required such as in the lubrication of traction motor bearings, wheel bearings on cars with disc brakes, steelmill bearings, ball joints, slow moving bearings and the like. To alleviate this deficiency, several methods have, heretofore, been proposed for producing grease compositions which will exhibit the desired extreme pressure properties and such methods include the use of various "extreme pressure" additives. Additives which have been proposed include chlorinated compounds such as chlorinated waxes, lead-sulfur systems, heavy metal sulfides (solid lubricants) and soluble phosphorus-sulfur systems. While these systems do provide some effectiveness in extreme-pressure applications, they do have some drawbacks. In this regard the chlorinated compounds have not been widely used since they can result in undesirable corrosion and the lead-sulfur systems generally have limited use because of the adoption of recent environmental protection standards.